<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    .active {
      color: red;
    }
  </style>
</head>
<body>

<div id="app">
  <ul>
    <li v-for="(item, index) in movies"
        :class="{active: currentIndex === index}"
        @click="liClick(index)">
      {{index}}.{{item}}
    </li>

    <!--<li :class="{active: 0===currentIndex}"></li>-->
    <!--<li :class="{active: 1===currentIndex}"></li>-->
    <!--<li :class="{active: 2===currentIndex}"></li>-->
    <!--<li :class="{active: 3===currentIndex}"></li>-->
  </ul>
</div>

<script src="../js/vue.js"></script>
<script>
  const app = new Vue({
    el: '#app',
    data: {
      movies: ['海王', '海贼王', '加勒比海盗', '海尔兄弟'],
      currentIndex: 0
    },
    methods: {
      liClick(index) {
        this.currentIndex = index
      }
    }
  })
</script>

</body>
</html>